如何在SWIG界面文件中检查Lua版本? [英] How to check Lua version in SWIG interface file?

问题描述

我具有以下功能，仅在Lua版本等于或小于5.1时才想使用.

I have the below function which I would like to use only when the Lua version is equal to, or smaller than 5.1.

所以我在myBindings.i文件中将其写为以下内容:

So I wrote it like the following in myBindings.i file:

/* used to backport lua_len to Lua 5.1 */
#if LUA_VERSION_NUM <= 501
%{
static void lua_len(lua_State *L, int i) 
{
    switch (lua_type(L, i)) 
    {
        case LUA_TSTRING:
            lua_pushnumber(L, (lua_Number)lua_objlen(L, i));
            break;
        case LUA_TTABLE:
            if (!luaL_callmeta(L, i, "__len"))
            lua_pushnumber(L, (lua_Number)lua_objlen(L, i));
            break;
        case LUA_TUSERDATA:
            if (luaL_callmeta(L, i, "__len"))
            break;
        default:
        luaL_error(L, "attempt to get length of a %s value",
                   lua_typename(L, lua_type(L, i)));
  }
}
%}
#endif

但是，当我编译代码时，编译器不会跳过Lua 5.3中的lua_len函数.

However when I compile the code, the compiler doesn't skip the lua_len function in Lua 5.3.

如何根据版本信息向编译器公开lua_len函数?

how can I expose lua_len function to the compiler depending on the version info?

推荐答案

TL; DR::您必须将预处理程序宏移动到文字块%{ ... %}中.

TL;DR: You have to move the preprocessor macros inside the literal block %{ ... %}.

在这种情况下

#if CONDITION
%{
...
%}
#endif

CONDITION由SWIG评估. SWIG不了解宏LUA_VERSION_NUM，因为它与先验接口无关(即，您还可以生成LUA_VERSION_NUM没有任何意义的Python接口).

the CONDITION is evaluated by SWIG. SWIG does not know about the macro LUA_VERSION_NUM because it is a priori interface agnostic (i.e. you could also generate a Python interface where LUA_VERSION_NUM has no meaning).

在变体中

%{
#if CONDITION
...
#endif
%}

SWIG将把文字块内的所有内容转发到接口文件.字面上会发生这种情况，而无需SWIG进行任何进一步检查，因此预处理器宏将保持不变. C ++编译器将包含<lua.hpp>并在其中找到LUA_VERSION_NUM的定义，因此该宏将具有预期的作用.

SWIG will forward everything inside the literal block to the interface file. This will happen literally without any further inspection by SWIG, so preprocessor macros will be untouched. The C++ compiler will include <lua.hpp> and finds a definition of LUA_VERSION_NUM there, so the macro will have its intended effect.

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